In 1951, Heinlein made use of the autocab in one of his juvenile novels Between Planets.

In 1965, Philip K. Dick described an autonomic cab in his classic The Three Stigmata of Palmer Eldritch.

In 1976, Larry Niven came pretty close with his bubble car from A World Out Of Time.

In 1976, Arthur C. Clarke wrote in detail about an automatic control car in his excellent Imperial Earth.

In 2006, Alan Dean Foster wrote about an automated taxi in his excellent novel Sagramanda.

Note: This list does not include references to vehicles that are driven by robots, as opposed to vehicles which are by themselves autonomous, nor does it include autonomous flying vehicles. I've also skipped movie and TV references - so I'll just leave this here for fans of KITT ;-)